Create an external table

You can create an external table by using the CREATE EXTERNAL TABLE statement. When you create an external table, you must specify the path of the data file and the format of the data file to read data from the external file.

Privilege requirements

To create an external table, the current user must have the CREATE privilege. For more information about how to view the privileges of the current user, see View user privileges.

Create an external table

The following example shows the syntax for creating an external table:

CREATE EXTERNAL TABLE table_name (column_definition_list)
    LOCATION = 'file_name'
    {FORMAT = (format_type_options)
     | PROPERTIES = (properties_type_options)}
    [PARTITION BY (column_name [, column_name ...])]
    [PARTITION_TYPE = USER_SPECIFIED]
    [PATTERN = 'regex_pattern']
    [AUTO_REFRESH = 'xxx'];

column_definition_list:
    column_definition [, column_definition ...]

column_definition:
    column_name column_type [AS (metadata$filecol{N})]

format_type_options:
    type_csv_option
    | type_parquet_option
    | type_orc_option

type_csv_option:
    TYPE = 'CSV'
    LINE_DELIMITER = '<string>' | <expr>
    FIELD_DELIMITER = '<string>' | <expr>
    ESCAPE = '<character>' | <expr>
    FIELD_OPTIONALLY_ENCLOSED_BY = '<character>' | <expr>
    ENCODING = 'charset'
    NULL_IF = ('<string>' | <expr>, '<string>' | <expr> ...)
    SKIP_HEADER = <int>
    SKIP_BLANK_LINES = {TRUE | FALSE}
    TRIM_SPACE = {TRUE | FALSE}
    EMPTY_FIELD_AS_NULL = {TRUE | FALSE}
    IGNORE_LAST_EMPTY_COLUMN = {TRUE | FALSE}

type_parquet_option:
    TYPE = 'PARQUET'

type_orc_option:
    TYPE = 'ORC'

properties_type_options:
    type_odps_option

type_odps_option:
    TYPE = 'ODPS'
    ACCESSID = '<string>'
    ACCESSKEY = '<string>'
    ENDPOINT = '<string>',
    PROJECT_NAME = '<string>',
    SCHEMA_NAME = '<string>',
    TABLE_NAME = '<string>',
    QUOTA_NAME = '<string>',
    COMPRESSION_CODE = '<string>',
    API_MODE = {"tunnel_api" | "storage_api"},
    SPLIT = {"byte" | "row"}

The parameters are described as follows:

• col_name col_type [AS (metadata$filecol{N})]: specifies the columns of the external table. You can set the AS (metadata$filecol{N}) parameter to manually specify column mapping.

  The column types of an external table are the same as that of a regular table. For more information about the data types supported by OceanBase Database in MySQL mode and details about these data types, see Overview of data types.

  By default, columns in the external file are automatically mapped to those in the external table in sequence. In other words, the first column in the external table is automatically mapped to the first column in the external file.

  For example, in the following example, the C1 column in the ext_t1 external table is automatically mapped to the first column in the external file; the C2 column is automatically mapped to the second column in the external file.

  CREATE EXTERNAL TABLE ext_t1 (
    C1 int,
    C2 int
    )
    LOCATION = 'oss://$ACCESS_ID:$ACCESS_KEY@$HOST/tpch_1g_data/lineitem/'
    FORMAT = (
    TYPE = 'CSV'
    FIELD_DELIMITER = '|'
    );
  

  If the order of columns in the external file is different from that in the external table, you can use the metadata$filecol{N} pseudo-column to specify that a column in the external table be mapped to the Nth column in the external file. Note that the columns in the file are numbered starting from 1.

  For example, in the following example, C1 int AS (metadata$filecol2) specifies that the C1 column in the ext_t2 external table be mapped to the second column in the file; C2 int AS (metadata$filecol4) specifies that the C2 column in the ext_t2 external table be mapped to the fourth column in the external file.

  CREATE EXTERNAL TABLE ext_t2 (
              C1 int AS (metadata$filecol2),
              C2 int AS (metadata$filecol4)
    )
    LOCATION = 'oss://$ACCESS_ID:$ACCESS_KEY@$HOST/tpch_1g_data/lineitem/'
    FORMAT = (
    TYPE = 'CSV'
    FIELD_DELIMITER = '|'
    );
  

  Notice

  If you want to manually specify column mapping, automatic column mapping will fail and all columns must be mapped manually.

• LOCATION = 'file_name': specifies the path where the external file is stored. In most cases, the data files of an external table are stored in a dedicated directory, which can contain subdirectories. When you create an external table, the database automatically collects all files in the directory.

  Two formats are supported:

  • Local location format: LOCATION = '[file://] local_file_path'

    • local_file_path: can be a relative path or an absolute path. If you enter a relative path, the current directory must be the installation directory of OceanBase Database.

      Notice

      The local_file_path parameter must specify a directory rather than a file. If you want to specify a single file, you need to set the LOCATION parameter to the directory that contains the file and set the PATTERN parameter to the file.

    • For scenarios that use the local location format, if you configure the value of the secure_file_priv variable to a path that OceanBase Database can access, the value must be the parent directory of local_file_path, namely, local_file_path must be a subdirectory of the secure_file_priv path.

      The secure_file_priv variable specifies the path that OceanBase Database can access when you import data to a file or export data from a file. For more information about the secure_file_priv variable, see secure_file_priv.

  • Remote location format: LOCATION = '{oss|S3}://$ACCESS_ID:$ACCESS_KEY@$HOST/remote_file_path'

    $ACCESS_ID, $ACCESS_KEY, and $HOST are required access parameters for accessing Alibaba Cloud OSS, AWS S3, and object storage services that support the S3 protocol. These sensitive access parameters are stored in the system tables of the database in encrypted form.

    Notice

    When you use object storage as the data source, make sure that the values of the parameters in the object storage path are composed of uppercase and lowercase letters, digits, and the following special characters: /-_$+=. Otherwise, the setting may fail.

• TYPE = 'CSV': specifies the format of CSV external files.

• TYPE: specifies the type of the external file.

• LINE_DELIMITER: specifies the line delimiter of the file. If this parameter is not specified, the default value LINE_DELIMITER='\n' takes effect.

• FIELD_DELIMITER: specifies the field delimiter of the file. If this parameter is not specified, the default value FIELD_DELIMITER='\t' takes effect.

• ESCAPE: specifies the escape character of the file. For example, ESCAPE ='*' indicates that the asterisk (*) is the escape character, which replaces the default escape character (). If this parameter is not specified, the default value ESCAPE ='\' takes effect.

• FIELD_OPTIONALLY_ENCLOSED_BY: specifies the characters that enclose the field values in the file. For example, ESCAPE = '"' indicates that the values are enclosed in double quotation marks. If this parameter is not specified, the default value takes effect.

  Notice

  When the external table data file contains NULL values (not the string NULL, that is, not "NULL"), you must explicitly configure the FIELD_OPTIONALLY_ENCLOSED_BY parameter, and its value cannot be empty.

• ENCODING: specifies the character set encoding used by the file. For more information about the character sets supported in MySQL mode, see Character sets. If this parameter is not specified, the default value UTF8MB4 takes effect.

• NULL_IF: specifies the strings that are treated as NULL values. If this parameter is not specified, the default value takes effect.

• SKIP_HEADER: specifies the number of lines to skip in the file header. If this parameter is not specified, the file header is not skipped by default.

• SKIP_BLANK_LINES: specifies whether to skip blank lines. If this parameter is not specified, the default value FALSE takes effect.

• TRIM_SPACE: specifies whether to remove leading and trailing spaces from fields in the file. If this parameter is not specified, the default value FALSE takes effect.

• EMPTY_FIELD_AS_NULL: specifies whether empty strings are treated as NULL values. If this parameter is not specified, the default value FALSE takes effect.

• IGNORE_LAST_EMPTY_COLUMN: specifies whether to ignore the empty field at the end of a line if the line ends with an empty field (when a column separator appears before the row separator). The default value is TRUE, indicating that the last empty field is ignored.

  Note

  For V4.3.5, IGNORE_LAST_EMPTY_COLUMN is supported starting from V4.3.5 BP2.

• TYPE = 'PARQUET': defines the external file format as PARQUET.

• TYPE = 'ORC': specifies that the external file format is ORC.

• TYPE = 'ODPS': Specifies that the external file format is ODPS. Also includes the following fields:

  • ACCESSID: specifies the AccessKey ID of your Alibaba Cloud account for authentication.

  • ACCESSKEY: specifies the AccessKey Secret corresponding to the AccessKey ID for authentication.

  • ENDPOINT: specifies the connection address for the ODPS service.

  • PROJECT_NAME: specifies the name of the target ODPS project.

  • SCHEMA_NAME: (optional). Specifies the schema name in ODPS.

  • TABLE_NAME: specifies the target table name in ODPS.

  • QUOTA_NAME: (optional). Specifies the quota to use.

  • COMPRESSION_CODE: (optional). Specifies the compression format of the data source. Supports ZLIB, ZSTD, LZ4, and ODPS_LZ4. If not set, disables compression.

  • API_MODE: Specifies the API mode used to access ODPS. Possible values:

    Note

    For OceanBase Database V4.3.5, parameters API_MODE and SPLIT are supported starting from V4.3.5 BP3.

    • tunnel_api (default value):

      • Does not require special network configuration: Suitable for all deployment scenarios. OceanBase Database and MaxCompute do not need to be in the same Virtual Private Cloud (VPC).

      • Does not require additional MaxCompute permissions: Only needs AccessKey ID and AccessKey Secret for authentication. Does not require MaxCompute Storage API permissions.

      • Is suitable when:

        • OceanBase Database and MaxCompute are not deployed in the same VPC.
        • MaxCompute Storage API is not enabled.
        • Data transfer does not have strict latency requirements.

    • storage_api:

      • Requires OceanBase Database and MaxCompute to be deployed in the same VPC for low-latency, high-throughput data transfer.

      • Requires Storage API permission to be enabled in MaxCompute, and the AccessKey to have the necessary permissions.

      • Is suitable when:

        • OceanBase Database and MaxCompute are in the same VPC network.
        • MaxCompute Storage API is enabled.
        • Data volume is large or real-time requirements are high.

  • SPLIT: When using storage_api, specifies whether to split tasks by byte or row for assignment to different threads. If the byte size of each row in a table varies greatly, setting SPLIT to byte does the splitting by byte; otherwise, setting it to row does the splitting by row.

• PATTERN: specifies the regular pattern string to filter files in the directory specified by LOCATION. For each file in the directory specified by LOCATION, if the file matches the pattern string, the external table can access the file. Otherwise, the external table skips the file. If this parameter is not specified, the external table can access all files in the directory specified by LOCATION by default.

Assume that a data.csv file exists in the /home/admin/oceanbase/ directory on your local machine, and the file contains the following data.

1,"lin",98
2,"hei",90
3,"ali",95

1. On the OBServer node, the tenant administrator connects to the MySQL tenant of the cluster through the local Unix socket.

   Here is an example of the connection:

   obclient -S /home/admin/oceanbase/run/sql.sock -uroot@sys -p********
   

   For more information about how to connect to OceanBase Database through a local Unix socket, see secure_file_priv.

2. Configure the path /home/admin/oceanbase/ that the database can access.

   SET GLOBAL secure_file_priv = "/home/admin/oceanbase/";
   

   After the command is executed, you need to restart the session for the modification to take effect.

3. Reconnect to the database and create an external table named ext_t3.

   CREATE EXTERNAL TABLE ext_t3(id int, name char(10),score int)
   LOCATION = '/home/admin/oceanbase/'
   FORMAT = (
   TYPE = 'CSV'
   FIELD_DELIMITER = ','
   FIELD_OPTIONALLY_ENCLOSED_BY ='"'
   )
   PATTERN = 'data.csv';
   

After the external table is created, you can use the SHOW CREATE TABLE statement to view the table definition, just like that for a regular table.

SHOW CREATE TABLE ext_t3;

The query result is as follows:

+--------+------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
| Table  | Create Table                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                           |
+--------+------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
| ext_t3 | CREATE EXTERNAL TABLE `ext_t3` (
  `id` int(11) GENERATED ALWAYS AS (metadata$filecol1),
  `name` char(10) GENERATED ALWAYS AS (metadata$filecol2),
  `score` int(11) GENERATED ALWAYS AS (metadata$filecol3)
)
LOCATION='file:///home/admin/oceanbase/'
PATTERN='data.csv'
FORMAT (
  TYPE = 'CSV',
  FIELD_DELIMITER = ',',
  FIELD_OPTIONALLY_ENCLOSED_BY = '"',
  ENCODING = 'utf8mb4'
)DEFAULT CHARSET = utf8mb4 ROW_FORMAT = DYNAMIC COMPRESSION = 'zstd_1.3.8' REPLICA_NUM = 1 BLOCK_SIZE = 16384 USE_BLOOM_FILTER = FALSE TABLET_SIZE = 134217728 PCTFREE = 0 |
+--------+------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
1 row in set 

You can also access the external table like a regular table. When you query an external table, the system reads the external file through the driver of the external table and parses the file according to its format. Then it converts the parsed data into internal data types of OceanBase Database and returns the data rows. Here is an example of querying the external table lineitem that is created just now.

SELECT * FROM ext_t3;

The query result is as follows:

+----+------+-------+
| id | name | score |
+----+------+-------+
|  1 | lin  |    98 |
|  2 | hei  |    90 |
|  3 | ali  |    95 |
+----+------+-------+
3 rows in set

You can also combine an external table with a regular table for query operations. Assume that a regular table named info exists in the current database, and the table contains the following data:

+------+--------+------+
| name | sex    | age  |
+------+--------+------+
| lin  | male   |    8 |
| hei  | male   |    9 |
| li   | female |    8 |
+------+--------+------+
3 rows in set

Here is an example of combining the external table ext_t3 with the regular table info for query operations.

SELECT info.* FROM info, ext_t3 WHERE info.name = ext_t3.name AND ext_t3.score > 90;

The query result is as follows:

+------+--------+------+
| name | sex    | age  |
+------+--------+------+
| lin  | male   |    8 |
| li   | female |    8 |
+------+--------+------+
2 rows in set

For more information about queries, see Read data.

Create an ODPS Java SDK external table

To create an ODPS Java SDK external table, you need to use OceanBase Database in an environment with the Java SDK installed. For detailed information on setting up the Java SDK environment, see Deploy the Java SDK environment for OceanBase Database.

An example of creating an ODPS Java SDK external table is as follows:

CREATE EXTERNAL TABLE lineitem(
    l_orderkey BIGINT,
    l_partkey BIGINT, 
    l_suppkey BIGINT,
    l_linenumber BIGINT, 
    l_quantity DECIMAL(15,2), 
    l_extendedprice DECIMAL(15,2),
    l_discount DECIMAL(15,2),
    l_tax DECIMAL(15,2),
    l_returnflag CHAR(1),
    l_linestatus CHAR(1), 
    l_shipdate DATE, 
    l_commitdate DATE, 
    l_receiptdate DATE,
    l_shipinstruct CHAR(25),
    l_shipmode CHAR(10),
    l_comment VARCHAR(44))
    PROPERTIES = (
        TYPE = 'ODPS'
        ACCESSID = '***********'
        ACCESSKEY = '***********'
        ENDPOINT = 'http://service.cn-hangzhou.maxcompute.aliyun.com/api',
        PROJECT_NAME = 'bigdata_public_dataset',
        SCHEMA_NAME = 'tpch_10g',
        TABLE_NAME = 'lineitem',
        QUOTA_NAME = '',
        COMPRESSION_CODE = '',
        API_MODE = "storage_api",
        SPLIT = "byte"
        ); 

Considerations

• An external table can only be queried, and you cannot perform DML operations on it.

• When you query an external table, if the external file accessed by the table has been deleted, the system does not return an error, but instead returns an empty result set.

• The external file system manages the files accessed by an external table. If the external storage system is unavailable, an error is returned when you query the external table.

What to do next

When you create an external table, the system saves the file list that matches the PATTERN in the LOCATION specified in the LOCATION to the system table of OceanBase Database. During a scan, the system accesses external files based on this list. If other files are added to the external directory, you must perform an operation to update the external table to add the new files to the file list of the external table. For more information, see External file management.

After you create an external table, you can drop it. The statement for dropping an external table is the same as that for dropping a regular table. You can use the DROP TABLE statement to drop an external table. For more information, see Drop a table.

References

• Overview of external tables

• Manage external files